In recent years, a laminate film (also referred to as a laminate sheet) is used as an outer covering member for covering a power generation element of a battery for decreasing a weight of the battery, and decreasing a thickness of the battery. The laminate film has, for example, a structure in which an aluminum foil is stacked between a resin film and a resin film.
As a conduction (continuity) test method between this laminate film and the internal power generation element, there is a method of inserting a metal needle on a surface of the outer member of the laminate film, and measuring a resistance between this needle and a lead electrode extending from the power generation element (patent document 1).
In a normal laminate-packed battery, the internal power generation element and the laminate film are insulated so as not to leak the current to the laminate film which is the outer covering member (package) (cf. background art of the patent document 1). By applying the conventional art, it is possible to test the insulating state between the power generation element and the laminate film by inserting the needle from the surface of the laminate film, and measuring the resistance between this needle and the lead electrode extending from the power generation element.
However, the laminate film has a structure in to which the aluminum foil is sandwiched between the two resin films. Accordingly, when the needle is inserted from above on the surface of the laminate film, that is, the resin film, the needle may drag and wound the resin. In this case, the resin is wound around the needle, so that the needle and the aluminum foil are not contacted with each other. Consequently, it is not understand whether or not the power generation element and the aluminum foil of the laminate film are conducted with each other. The reliability of the conduction test is decreased. That is, even when the power generation element and the aluminum foil of the laminate film are conducted (short-circuited), the test result represents that there is no conduction.